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Radiochemical measurements on neutron sources

Abstract

The investigations described in this thesis relate to the development of an accurate method for the comparison of strengths of weak neutron sources with different spectra. This is part of a programme for the establishment of an absolute neutron standard. A detailed review of the preparation and properties of various portable neutron sources at present in use has been presented. The advantages of the stoichiometric compound, Radium Beryllium Fluoride (RaBeP4 ), as a reproducible neutron standard have been discussed. A survey of the existing methods for the absolute and relative strengths of neutron sources has been made and the need for an accurate method for the comparison of strengths of weak neutron sources with different spectra has been pointed out. The principle of thermalisation followed by physical integration, with a solution of indium sulphate, has been employed for developing a new method for the measurements of relative neutron source strengths. Using this method, the relative strength of the proposed RaBeF 4 standard source with respect to a standard radium-I--beryllium source was determined with an accuracy better than 1%. When the absolute strength of the latter source is determined, the absolute strength of the RaBeF4 source can be given with this accuracy. Investigations were also carried out to estimate the extent of loss of fast neutrons from the radium-(-beryllium sources by reactions with oxygen and sulphur present in aqueous moderator solutions normally used for neutron strength comparisons. The principle involved was to compare the relative strengths in an aqueous medium and an organic medium containing less oxygen, but having the seine hydrogen and indium contents. Since no systematic errors are involved, the value obtained is considered more reliable.